This invention relates to a new and improved resistor element for use at elevated temperatures.
Resistor elements suitable for use in spark plugs must have good mechanical and electrical stability at high temperatures, a wide operating temperature range, uniform resistance values, and good suppression of high frequency oscillations associated with spark discharge in ignition systems.
Prior art resistor compositions consisting of carbon or graphite dispersed in a resinous binder are inexpensive, but have a limited temperature range and a high voltage coefficient of resistance. Vitreous type carbon resistor elements, formed from clay, talc and a refractory material having carbon distributed therein, have been used extensively. However, it is difficult to prepare such resistors having uniform resistance values. In an attempt to overcome difficulties encountered with the use of carbon, other resistor composition systems have been suggested. For example, U.S. Pat. Nos. 2,864,773 and 2,969,582 disclose the use of titanate and stanno-titanate type materials modified to obtain desired electrical characteristics.